In the production of pressed board and particleboard from fibrous materials to which thermally activated or thermosetting binders have been added or which utilize intrinsic binder substances, the mass of fiber and/or particles is generally formed into the shape of a rectangular mat and subjected to compaction in a platen press which may be a single-level or multilevel press.
The mats can be handled by conveyors in which the mat is formed on and deposited on the surface of the conveyor directly. To facilitate introduction of the mat into the press, it may be placed upon a flexible metal sheet or underlay which can be associated with a bar at the leading edge or head of the underlay so that the transfer of the sheet with the mat thereon onto further conveyors or onto the bed plate or a platen of the press, is facilitated.
The bar can be used as a spacer between the pressing surfaces to determine the degree of compaction and hence the thickness of the pressed body.
Particleboard of the aforedescribed type can be composed of wood and/or other cellulosic fibers or wood particles in the form of sawdust or chips and binders such as phenolic resins may be mixed with the particles before or after they are formed into the mats.
The pressing is generally effected under heat and with pressure calibrated to allow the finished board to have the desired thickness and density. Low-density board may be used for insulation, decorative and partitioning purposes, while more dense board may be used for a variety of structural or load-bearing purposes.
Particleboard made in the aforedescribed manner may be laminated to decorative or protective layers which can be applied to the mat in the form of foils before the mat is introduced into the press and various textures may be imparted to the board surface to imitate natural wood patterns or the like.
The press sheets can be composed of stainless steel or other materials to which the mat does not readily stick and to which the board, upon hot-pressing, does not adhere.
Upon completion of the pressing operation, the press sheets and the associated head bars are generally recycled to the station at which they were originally applied to the underside of the mat.
In the handling of mats in the aforedescribed manner, it has been proposed heretofore to deliver the mat to the latter station on a feed conveyor whose discharge edge was formed as a nose overhanging a drum which delivered the press sheet or underlay and the head bar attached at the leading edge to the sheet, to the region between the discharge edge of the feed conveyor and the pick-up end of a receiving or transfer conveyor which carried the mat to the press.
Thus an apparatus of this type (see German patent No.22 36 937) comprised a feed conveyor belt upon which the rectangular mat was formed or onto which this mat had previously been deposited directly, an intermediate storage drum for delivering the press sheet and its head bar, and a receiving conveyor upon which the sheet having the mat deposited thereon, was carried away.
The feed conveyor had its transfer end or nose extending toward and overhanging the point at which the drum carried the head bar and attached press sheet to the horizontal receiving plane of the receiving conveyor.
The drum was so constructed and arranged that each bar lay above the drum surface while the associated sheet lay upon the cylindrical drum surface, the drum having a receptacle likewise disposed above the drum surface for entraining the bar and, therewith, the sheet in the direction of drum rotation.
For ease in entrainment of the underlay, i.e. the combination of the head bar and the sheet or web, the head bar must be relatively thick and rigid and thus projects well above the flexible layer on the drum surface. The receiving conveyor is formed with entraining members which engage this bar.
Since the bars lie above the periphery of the drum and the bar-engaging entrainers of the drum also project above the periphery, the displacement planes of the feed conveyor and the receiving conveyor must be disposed above a tangent plane to the drum surface at its apogee so as to clear the projections from the drum which entrain the bars.
Since the discharge end of the feed conveyor overhanging the drum also has a thickness which is not insignificant, its conveyor plane must be spaced further above the tangent plane by a corresponding amount.
As a result, when the mat is deposited on the underlayment, the transfer is effected over a downward step which can be damaging to the mat and can generate folds, wrinkles or dislocations therein which appear at least in part in the finished product. Since this effect is most pronounced at high transfer speeds, the operating speed of the apparatus must be limited.